1. Field of the Invention
The present invention relates to a webbing retractor, and in particular, to a webbing retractor which can impede rotation of a spool in a webbing pull-out direction at a time when a vehicle rapidly decelerates or at a time when the webbing is rapidly pulled-out.
2. Description of the Related Art
Generally, in a webbing retractor, a webbing is wound in a roll form on a hollow cylindrical spool supported at a frame which is formed in a substantial U-shape as seen in plan view and which is fixed to a vehicle. Usually, the webbing can be freely taken-up or pulled-out due to the spool rotating freely. Further, in the webbing retractor, a WSIR (webbing sensitive inertia reel) or a VSIR (vehicle sensitive inertia reel) is utilized in order to impede pulling-out of the webbing when a rapid deceleration of the vehicle or a rapid pulling-out of the webbing is sensed.
A WSIR or a VSIR is equipped with a lock function to impede rotation of the spool in the webbing pull-out direction, in order to impede pulling-out of the webbing in the above-described cases. An example of such a lock mechanism is the lock mechanism disclosed in Japanese Patent Application (JP-A) No. 5-246303 in which a main pawl and a back-up pawl (lock plate) are disposed at the both sides of a reel shaft (spool), and due to the main pawl and the back-up pawl engaging with teeth (lock teeth) formed at a frame, rotation of the reel shaft in the webbing pull-out direction is impeded. In such a conventional lock mechanism, rotation of the reel shaft in the webbing pull-out direction can be reliably impeded in predetermined cases, and the webbing retractor can be made lighter-weight (e.g., the main pawl and the back-up pawl can be made thinner) because the load at the time of locking is dispersed at the main pawl and the back-up pawl which are provided at the both sides of the reel shaft.
In the above-described conventional webbing retractor, when placing the main pawl and the back-up pawl at the both ends of the reel shaft, in a state in which the main pawl is inserted into one end of a joint pin, the joint pin is inserted into a through hole formed in the spool. Further, in this state, the back-up pawl is mounted to the other end portion of the joint pin. Namely, at the time that three parts which are the joint pin, the main pawl and the back-up pawl are assembled to the spool, they are connected so as to be interlocking.
Thus, the workability in assembling the main pawl and the back-up pawl to the reel shaft is poor. Moreover, the number of parts forming the lock mechanism is large, and accordingly, there is the problem that the number of assembly processes is large.
In view of the above circumstances, an object of the present invention is to provide a webbing retractor in which the structure of a lock plate can be simplified, it is easy to assemble a lock plate to a spool, and workability is improved.
In order to achieve the above object, a webbing retractor relating to the present invention comprises: a spool which is tube-shaped and on which a webbing is taken-up and from which the webbing is pulled-out; a cut-out portion formed over an entire length of an outer surface of the spool along a rotational axis of the spool, a bottom portion of the cut-out portion being circular-arc-shaped; a frame which is fixed and held at a vehicle, and which rotatably supports the spool between a pair of leg pieces, and at which lock teeth are formed at an inner surface of an opening of each leg piece; and a lock plate having a pair of pawls formed so as to be engageable with the lock teeth, and a connecting shaft which has a circular cross-section and which connects the pair of pawls, and due to the connecting shaft being inserted into and disposed in the cut-out portion, the pair of pawls are disposed so as to oppose the lock teeth at both end portions of the spool, and in a predetermined case, due to due to the pair of pawls engaging with the lock teeth, the lock plate impedes rotation of the spool in a webbing pull-out direction.
In the above-described webbing retractor, usually, the lock plate is disposed so as to oppose the lock teeth, and the lock plate and the lock teeth are in anon-engaged state. Thus, rotation of the spool is not limited, and the webbing can be freely taken-up and pulled-out.
On the other hand, in a predetermined case such as, for example, at a time when the vehicle rapidly decelerates or the webbing is rapidly pulled-out, the lock plate, which is provided with the pair of pawls disposed at the both end portions of the spool, engages with the lock teeth formed at the pair of leg pieces forming the frame, and rotation of the spool in the webbing pull-out direction is thereby hindered.
Here, when the lock plate, which is provided with the pair of pawls disposed at the both end portions of the spool, is assembled to the spool, first, the pawls are connected to the both ends of the connecting shaft, and the lock plate is formed as a single part. When the lock plate is formed, the connecting shaft is inserted into the spool from the opening, along the spool rotating shaft, of the cut-out portion which is formed along the entire length of the outer surface of the spool. When the connecting shaft is inserted into the spool, due to the lock plate being appropriately rotated around the connecting shaft, the lock plate is disposed at a predetermined position. In this state, other parts, such as a V gear forming a WSIR or a VSIR, or the like, are assembled.
In this way, in the webbing retractor of the present invention, there is no need to mount a pawl in the state in which a connecting shaft is inserted into a through hole of a spool, as in the conventional art. By inserting the connecting shaft of the lock plate, which is a single part, into the spool from the cut-out portion, the lock plate can be assembled to the spool. Thus, the structure of the lock plate can be simplified, the assembly of the lock plate to the spool is easy, and workability improves.
In the webbing retractor relating to the present invention, preferably, at the lock plate, the pair of pawls and the connecting shaft are formed integrally.
In this webbing retractor, the lock plate, which has the pair of pawls and the connecting shaft, is formed integrally (integrally molded) as a single part in a part machining step. Thus, at the time when the lock plate is assembled to the spool, there is no need to connect the pawls to the both ends of the connecting shaft. As a result, when assembling the lock plate to the spool, it suffices to insert the connecting shaft of the lock plate, which is a single part, into the spool from the cut-out portion of the spool, and to rotate the lock plate appropriately.
Further, because the lock plate is molded integrally, there are no limits on the configuration accompanying the formation of the portions which connect the pawls and the connecting shaft. Thus, the degrees of freedom of the shape (design) of the lock plate can be increased. Moreover, the dimensional precision of the lock plate is provided by the precision of machining alone, and there is no need to consider the precision of assembly. Thus, constant dimensional precision can easily be obtained.
In this way, in the preferable webbing retractor of the present invention, the structure of the lock plate can be simplified even more, the assembly of the lock plate to the spool can be simplified even more, and workability improves.